Gearbox selector mechanism

ABSTRACT

A selector mechanism for a gearbox in which speed change couplers (28, 29) and a range change coupler (34) are operated by the same selector lever (47). Lever (47) operates the speed change couplers to engage a plurality of drive speeds when moved from a neutral plane to speed selection positions (1, 2, 3, 4) in a speed change gate and operates the range change couplers when moved to discrete range change positions (H,L). The selector mechanism is arranged so that on movement of the selector lever (47) out of the speed change gate towards a desired range change position (H, L) the range change coupler (34) is moved towards an engaged position for the desired range and on movement of the selector lever back towards the speed change gate from the desired range change position the movement of the range change coupler (34) is completed to engage the desired range.

This invention relates to gearbox selector mechanisms and in particularsuch mechanisms which require the sequential operation of separatecouplers within the gearbox by a single selector member. An example ofsuch a mechanism is in a tractor gearbox where speed change couplers andrange change couplers are required to be operated by a single selectormember in the form of a gear lever.

Various selector mechanisms have been proposed for such applications.For example, the mechanism disclosed in United Kingdom patent number1546461. However such mechanisms have produced relative complex gearlever shift patterns as shown by the double H-shift pattern of the abovepatent.

It is an object of the present invention to provide a selector mechanismsuitable for a gearbox in which a single selector member controls bothspeed and range changes and in which a simple selector member shiftpattern is achieved.

Thus according to the present invention there is provided a selectormechanism for a gearbox in which one or more speed change couplers andone or more range change couplers are operated by the same selectormember, said selector member operating the speed change coupler orcouplers to engage a plurality of drive speeds when moved from a neutralplane to speed selection positions in a speed change gate and operatingthe range change coupler or couplers when moved to discrete range changepositions, the mechanism being arranged so that on movement of theselector member out of the speed change gate towards a desired rangechange position the appropriate range change coupler is moved towards anengaged position for the desired range and on movement of the selectormember back towards the speed change gate from the desired range changeposition the movement of the said appropriate range change coupler iscompleted to engage the desired range.

In a preferred construction an H-shaped gate is used for the speedchange gate with the neutral plane bridging the arms of the H and therange change positions are provided in a plane parallel to the two speedchange arms of the H reached by an extension of the neutral plane of theH, the selector mechanism being arranged to move the appropriate rangechange coupler towards said engaged position on movement of the selectormember along the extension of the neutral plane during movement of theselector member towards the range change plane, during movement of theselector member towards the appropriate range change position in therange change plane, and on movement of the selector member back alongthe extension of the neutral plane on its way back to the speed changegate.

The movement of the appropriate range change coupler as the selectormember moves along the neutral plane extension towards the range changeplane may be achieved by contact between a first component moved by theselector member and a first cam formation associated with theappropriate coupler and the movement of the coupler during the returnmovement of the selector member back along the extension of the neutralplane may be achieved by contact between a second component moved by theselector member and a second cam formation associated with theappropriate coupler.

The first component may be a selector finger which is moved by theselector member to engage selector formations associated with the speedand range change couplers and the second component may comprise aninterlock member moved by the selector finger to allow movement of onlyone coupler at a time.

In a preferred construction the speed and range change couplers areoperated by selector forks mounted for sliding movement on a single railand the interlock member is mounted for pivotting about said singlerail.

One embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a vertical section through a tractor transmission which iscontrolled by a selector mechanism in accordance with the presentinvention;

FIG. 2 is a plan view of part of the selector mechanism of the presentinvention;

FIG. 3a shows one form of gear selector lever arrangement suitable foruse as part of the present invention;

FIGS. 3b and 3c show diagrammatically various selection positions of thelever arrangement of FIG. 3a;

FIG. 4 shows diagrammatically the selection gate of the leverarrangement of FIG. 3a;

FIG. 5 is a view in the direction of the arrow Q of FIG. 2.

FIG. 6 is a view in the direction of arrow P of FIG. 5;

FIG. 7 is a view in the same direction as FIG. 5 of a selector fork usedas part of the selector mechanism;

FIG. 8 is a view in the direction of the arrow M of FIG. 7.

FIG. 9 is a view in the direction of the arrow N of FIG. 7;

FIG. 10 is a perspective view of part of FIG. 7 in the direction ofarrow O, and

FIGS. 11a to 11g diagrammatically illustrate the sequence of movementsof the selector fork of FIG. 7 during a range of change selection.

The transmission shown in FIG. 1 comprises a main 4-speed change speedgear set X, a 2-speed high/low range change gear set Y, and an inputforward/reverse gear set Z.

The input gear set Z comprises a forward gear train in the form ofconstant mesh gears 10 and 11 and a reverse gear train in the form ofgear 12 and a reverse idler shaft shown schematically at 13 whose gears13a and 13b are in constant mesh with gears 11 and 12 respectively. Asynchromesh unit 14 with a coupling sleeve 15 is operational to provideforward drive to the transmission when the sleeve 15 is moved to theright (as viewed in FIG. 1) to connect the gear 10 with a transmissioninput shaft 9 which surrounds a power take-off (PTO) shaft 40.

In a similar fashion reverse drive is provided through the transmissionby moving the sleeve 15 to the left to couple the gear 12 with inputshaft 9 and to reverse the direction of rotation of gear 11 via theidler shaft 13.

Selection of forward and reverse drive is via a selector mechanism whichoperates on sleeve 15 and which is not shown since it forms no part ofthe present invention.

The main 4-speed change speed gear set X comprises 4 gears 16, 17, 18and 19 splined on a lay shaft 30 which surrounds the PTO shaft 40, thesegears are in constant mesh with gears 20,21,22 and 23 which are rotablemounted on two portions 24 and 25 of a transmission output shaft.Synchromesh units 26 and 27 having coupling sleeves 28 and 29respectively are provided for coupling gears 20, 21 and 22, 23 to theoutput shaft.

The high/low range change set Y comprises a gear 31 on lay shaft 30 anda gear 32 rotable mounted on output shaft portion 25. A furthersynchromesh unit 33 with a coupling sleeve 34 is provided for couplingeither gear 23 or 32 to the output shaft 25. When coupling sleeve 34 ismoved to the left, drive is transmitted to output shaft 25 via gear 23and the high range is engaged. With the coupling sleeve 34 moved to theright, drive is transmitted to the output shaft 25 via gear 32 from layshaft gear 31 and a low range is engaged.

With coupler 28 of gear set X moved to the left as shown in FIG. 1, afirst speed is obtained via gears 20 and 16 lay shaft 30 and then fromlay shaft 30 to output shaft 25 via either gears 19, 23 or 31, 32depending on the position of the range coupler 34.

Similarly, second and third speeds are obtained from gear set X whengears 21 and 22 are respectively coupled to shaft 24. These gearstransfer drive to layshaft 30 via gears 17 and 18 respectively and driveis again transmitted to output shaft 25 via either gears 19, 23 or 31,32.

A fourth speed is obtained when sleeve 29 is moved to the right tocouple gear 23 to shaft portion 24. Drive is then transmitted to shaftportion 25 either directly from gear in the high range by moving coupler34 to the left or via gears 23, 19, 31, 32 in the low range by movingcoupler 34 to the right.

The present invention, as will be described below, is concerned with theprovision of a selector mechanism which enables a single selector memberto operate the two speed change couplers 28, 29 and also the rangechange coupler 34.

Referring to FIG. 2, this shows schematically the selector forkarrangement in accordance with the present invention which is used tooperate couplers 28, 29 and 34. Selector forks 41, 42 and 43 operatecouplers 28, 29 and 34 respectively and are mounted for sliding on asingle fixed support rail 39. Each selector fork has a portion 41a, 42a,43a provided with a slot 41b, 42b, 43b which receives a selector finger44 (see FIGS. 3a, 3b, 3c) carried on the end of a rotable and axiallymovable selector shaft 45 which is controlled via a gear selector leverarrangement 46 in accordance with United Kingdom Patent No. 2136516.

Gear selector lever arrangement 46 has an upper lever 47 which ispivotally mouned at 48 for pivotting about on a ball mount and a lowerlever 49 which is pivotally mounted on a ball mount 50 which lies on thelongitudinal axis Z of selector shaft 45. The upper and lower levers areinterconnected by a cup 51 on upper lever 47 which is engaged by a partspherical member 52 on lower lever 49. Selector shaft 45 is providedwith a forked arm 53 which extends either side of the lower lever 49 andis pinned at 54 to the lower lever.

Upper lever 47 is movable in the selection gate shown in FIG. 4 in whichspeeds 1 to 4 are selected by movement of the lever in selection planesA and B in a conventional H-shaped gate with a neutral plane N and thehigh and low ranges are selected by movement of the upper lever topositions H and L in a range change plane R to one side of the speedselection gate.

As will be appreciated movement of lever 47 in direction X of FIGS. 4and 3b whilst in the neutral plane N moves selector finger 44 indirections W1 and W2 to pick-up slots 41b, 42b or 43b as will bedescribed in more detail below. With the lever 47 in plane A, the finger44 engages in slot 41b and lever 47 can be moved in direction Y of FIGS.4 and 3c to turn shaft 45 and hence move the end of finger 44 todisplace selector fork 41 in direction T of FIG. 2 to engage eitherspeed 1 or 2 depending on which position the lever 47 is moved to in thegate. Similarly, with the lever 47 in plane B the finger 44 engages inslot 42b and the lever 47 can be moved in direction Y to turn shaft 45to displace fork 42 in direction T and hence engage either speed 3 or 4depending on whether the lever 47 is moved to position 3 or 4 in thegate.

As can be seen from FIGS. 2 and 5 an interlock member 55, which preventsmovement of more than one of the selector forks 41, 42 or 43 at once, isalso pivotally mounted on rail 39. The interlock member has a portion 56which, when the lever 47 is moving in its neutral plane N to displacefinger 44 in direction W1 or W2, is engageable in slots 41b, 42b and aportion 57 which is engageable in slots 42b, 43b. As will be appreciatedand as is described in greater detail below, the interlock member 55 ispivotted about rail 39 by contact with the lower end 44a of finger 44.

Finger 44 is also provided with an upper projection 44b which engages acontrol gate 58 provided in gate member 59 (see FIG. 6). Gate 58 has acentral slot 60 along which the projection 44b moves when lever 47 is inits neutral plane N and two perpendicular slots 61 and 62 whichcorrespond to movement of the lever 47 in planes A and R respectively.As will be appreciated slots 61 and 62 ensure the correct positioning ofthe lower end 44a of finger 44 in slots 41b and 43b respectively duringselection of speeds 1 or 2 and ranges H or L respectively.

The present invention is concerned with the manner in which lever 47 isalso able not only to select speeds 1 to 4 but also the high and lowranges H and L. Basically this is achieved by arranging that as thelever 47 moves towards plane R from plane A, that is along portion S ofthe lever gate, the lower end 44a of selector finger 44 makes contactwith either cam surface 70 or 71 built into the sides of slot 43b tobegin axial displacement of the selector fork 43 in direction T alongrail 39. Further axial displacement of fork 43 occurs as the lever ismoved within plane R towards either the H or L positions and the finalmovement of fork 43 necessary to engage either the H or L range is madeas the lever 47 is moved back along portion S of the gate on its way tore-enter the speed selection part of the gate to select the operativespeed. In the embodiment to be described in detail, this final axialmovement is obtained by the contact of portion 57 of the interlockmember 55 with either cam surface 72 or 73 of the slot 43b as theinterlock member 55 is moved back through slot 43b by abutment of thelower end 44a of the FIG. 44 with the end of protion 56 of the interlockmember as the finger moves to engage either slot 41b or 42b to selectthe operative speed in gear set X.

FIGS. 7, 8, 9 and 10 show details of the slot 43b in selector fork 43and FIGS. 11a to 11g show the sequence of movements of selector fork 43involved in the selection of the high range H.

FIG. 11a shows the selector finger portion 44a making initial contactwith the cam surface 70 as the lever moves along portion S of the gate.As the lever continues along portion S of the gate the finger 44a movesto the FIG. 11b position and in so doing crosses the cam surface 70 anddisplaces the selector fork 43 to the left (in direction T) as a resultof the cam action between surface 70 and finger 44a.

Typically this results in a 5mm axial movement of selector fork 43 tothe left. When the lever 47 has completed its movement to plane R andreached position 80 of FIG. 4, the finger 44a is in the FIG. 11cposition with the interlock portion 57 clear of slot 57 (as also shownin FIG. 5).

The lever 47 is now moved from position 80 to the high range selectorposition H and the selector fork 43 is thus moved to the left of theFIG. 11d position by finger 44a to provide typically say another 10mm ofaxial movement of the selector fork in direction T. It is during thismovement that synchronisation takes place.

The vehicle operator now begins the return movement of the selectorlever 47 back towards the speed selection potion of the gate by movinglever 47 from position H to position 80. This results in the finger 44amoving from one end of slot 43b (FIG. 11d) the other (FIG. 11e) withoutany axial movement of the selector fork 43 occurring.

As the lever 47 moves from position 80 back along portion S of the gatethe finger 44a contacts portion 56 of the interlock member 55 and pivotsthe interlock member anti-clockwise as viewed in FIG. 5 to cause portion57 to re-enter slot 43b and make contact with cam surface 73 (FIG. 11f)to again axially displace selector fork to the left in direction Ttypically a further 5mm of axial movement is obtained as the FIG. 44amoves from the FIG. 11f to the FIG. 11g position thus completing theselection of the high range.

When lever 47 reaches position 81 in plane A, the finger 44a has clearedslot 43b (FIG. 11g) and interlock portion 57 is engaged in slot 43b toprevent displacement of the range selector fork 43.

Thus the above arrangement enables a typical total axial movement of20mm of selector fork 43 to be obtained by moving the selector fork 5mmbetween positions 81 and 80, 10mm between positions 80 and H and thefinal 5mm on the return between positions 80 and 81.

It will be appreciated that the low range is selected in a similarmanner with the finger 44a and selector fork 43 moving in the sequenceof events shown by FIGS. 11g to 11a and the utilisation of cam surfaces71 and 72.

A further benefit of the simple single lever selection arrangement ofthe present invention is that before any change can be made in theoperative high or low range, the lever 47 must be placed in the neurtralplane N thus ensuring that drive through the speed change gear set X isdisconnected during range changes.

I claim:
 1. A selector mechanism for a gearbox in which one or morespeed change couplers (28, 29) and one or more range change couplers(34) are operated by the same selector member (47), said selector memberoperating the speed change coupler or couplers (28, 29), to engage aplurality of drive speeds when moved from a neutral plane (N) to speedselection positions (1, 2, 3, 4) in a speed change gate and operatingthe range change couper or couplers (34) when moved to discrete rangechange positions (H, L), the mechanism being characterised in that onmovement of the selector member (47) out of the speed change gate (1, 2,3, 4) towards a desired range change position (H, L) the appropriaterange change coupler (34) is moved towards an engaged position for thedesired range and on movement of the selector member back towards thespeed change gate (1, 2, 3, 4) from the desired range change positionthe movement of the said appropriate range change coupler (34) iscompleted to engage the desired range.
 2. A selector mechanism accordingto claim 1 characterised in that an H-shaped gate is used for the speedchange gate (1, 2, 3, 4) with the neutral plane (N) bridging the arms ofthe H and the range change positions are provided in a plane (R)parallel to the two speed change arms (A, B) of the H reached by anextension (S) of the neutral plane of the H, the selector mechanismbeing arranged to move the appropriate range change coupler (34) towardssaid engaged position on movement of the selector member (47) along theextension (S) of the neutral plane (N) during movement of the selectormember (47) towards the range change plane (R), during movement of theselector member (47) towards the appropriate range change position (H,L) in the range change plane (R), and on movement of the selector member(47) back along the extension (S) of the neutral plane (N) on its wayback to the speed change gate (1, 2, 3, 4).
 3. A selector mechanismaccording to claim 1 or claim 2 characterised in that the movement ofthe appropriate range change coupler (34) as the selector member (47)moves along the neutral plane extension (S) towards the range changeplane (R) is achieved by contact between a first component (44) moved bythe selector member (47) and a first cam formation (70, 71) associatedwith the appropriate coupler (34) and the movement of the coupler duringthe return movement of the selector member (47) back along the extension(S) of the neutral plane (N) is achieved by contact between a secondcomponent (57) moved by the selector member and a second cam formation(72, 73) associated with the appropriate coupler (34).
 4. A selectormechanism according to claim 3 characterised in that the first componentis a selector finger (44) which is moved by the selector member (47) toengage selector formations (41b, 42b, 43b) associated with the speed andrange change couplers (28, 29, 34) and the second component is aninterlock member (57) moved by the selector finger (44) to allowmovement of only one coupler at a time.
 5. A selector mechanismaccording to claim 4 characterised in that the speed and range changecouplers (28, 29, 34) are operated by selector forks (41, 42, 43)mounted for sliding movement on a single rail (39) and the interlockmember (57) is mounted for pivotting about said single rail.